In a mobile communication system, signals are often interleaved during signal transmission in order to achieve bit error discretization.
Taking an Orthogonal Frequency Division Multiplexing (OFDM) system for example, information bit packets to be transmitted in each cell are sequentially coded, bit-interleaved, and modulated to obtain multiple modulation symbols, and the obtained multiple modulation symbols are then grouped into multiple symbol groups. The obtained multiple symbol groups are distributed to multiple channels, for example, each channel is corresponding to one or more channel elements (CEs), so that the multiple symbol groups are uniformly distributed to multiple CEs corresponding to different channels. Symbol interleaving is also performed on the multiple symbol groups distributed to the multiple channels, for example, an existing Pruned Bit-Reversal Interleaver (PBRI) is used to re-arrange the multiple symbol groups, and sequentially map the multiple symbol groups after symbol interleaving to corresponding physical resource positions (for example, to corresponding resource elements (REs) in physical downlink control channels (PDCCHs) according to a predefined corresponding relation between the symbol group order and the physical resource positions.
As all the cells perform symbol interleaving with the same interleaving sequence, that is, by using the same interleaving apparatus, the multiple symbol groups after symbol interleaving in each cell are arranged in the same order, so that different cells sharing the same physical resources may map the same symbol groups to the same physical resource position, thereby causing resource collisions. As a result, severe signal interference between the cells and degradation of the transmission performance of the system occur.
In order to solve the above problem, in the conventional art, each cell may also perform cyclic shift on the multiple symbol groups after symbol interleaving according to corresponding cell-specific shift steps, so that the multiple symbol groups after symbol interleaving in different cells sharing the same physical resources are arranged in most possible different orders; and the symbol groups mapped to the same physical resource position are not completely the same, thereby realizing interference randomization between the cells and reducing performance loss caused by interference between the cells.
However, the above method reduces the performance loss due to interference between the cells to some extent, as for the CEs, different cells may map all or a large part of the symbol groups in one or more CEs to the same physical resource position. That is to say, mapping all or a large part of the symbol groups in the same CE or different CEs to the same physical resource position, which causes collisions between the CEs. As a result, great interference between the cells occurs, and the effect of interference randomization is undesirable.
For example, sixteen symbol groups having serial numbers 0 to 15 are provided and distributed to four CEs corresponding to multiple channels. Each CE includes four symbol groups, that is, the symbol groups 0 to 3 belong to CE0, the symbol groups 4 to 7 belong to CE1, the symbol groups 8 to 11 belong to CE2, and the symbol groups 12 to 15 belong to CE3.
Symbol interleaving is performed on the sixteen symbol groups with a PBRI interleaving sequence {0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}, and the interleaver is adapted to interleave the total sixteen symbol groups in the four CEs.
It is assumed that the cell-specific cyclic shift steps are 0 and 1; and the two cells may map the symbol groups to corresponding physical resource positions in the following sequences:
Cell—1={0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}; and
Cell—2={8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15, 0}.
That is to say, Cell—1 maps the symbol group 0 and Cell—2 maps the symbol group 8 to the 1st physical resource position, Cell—1 maps the symbol group 8 and Cell—2 maps the symbol group 4 to the 2nd physical resource position, and the rest may be deduced similarly.
The symbol interleaver is mainly adapted to ensure that the number of the symbol groups in one CE that are mapped to the same physical resource position by different cells after symbol interleaving and cyclic shift is reduced, thereby achieving interference randomization.
If the serial numbers of the symbol groups in the above two sequences are replaced by the serial numbers of the CEs that the symbol groups belong to, the following sequences are obtained:
Cell—1={0, 2, 1, 3, 0, 2, 1, 3, 0, 2, 1, 3, 0, 2, 1, 3}; and
Cell—2={2, 1, 3, 0, 2, 1, 3, 0, 2, 1, 3, 0, 2, 1, 3, 0}.
It can be seen from the sequences replaced by serial numbers of the CEs that, Cell—1 maps the symbol groups of CE0 and Cell—2 maps the symbol groups of CE2 to the 1st, 5th, 9th, and 13th physical resource positions, Cell—1 maps the symbol groups of CE2 and Cell—2 maps the symbol groups of CE1 to the 2nd, 6th, 10th, and 14th physical resource positions, and the rest may be deduced similarly. Therefore, Cell—1 and Cell—2 respectively map all the symbol groups in CE0 and CE2 to the same physical resource positions, map all the symbol groups in CE2 and CE1 to the same physical resource positions, map all the symbol groups in CE1 and CE3 to the same physical resource positions, and map all the symbol groups in CE3 and CE0 to the same physical resource positions. Collisions of CE0 with CE2, CE2 with CE1, CE1 with CE3, and CE3 with CE0 may occur between the above two cells, interference randomization between the cells is not achieved, and the transmission performance of the system is also affected.